Kotlin has been around for about five years, but it finally reached the production-ready version 1.0 this year. Although it hasn't achieved the popularity of Scala, Groovy, or Clojure—the three most popular and mature (non-Java) JVM langauges—it has separated itself from the myriad other JVM languages. It originated at JetBrains—makers of the popular IntelliJ IDEA IDE.